Maybe I'm misreading something. How did you calculate this because:
Looking at a binomial probability sums table, I can tell you the answer is not 2. I think you need to recheck your math. If you need help, let me know. Thanks.
Oops! I did misread. I thought p=0.5. My mistake.
Anyway, the answer should be 1, because it's the closest positive integer answer that doesn't cause the binomial probability to go over 0.8.